The phase-field model coupled with the concentration field, temperature field and flow field is used to simulate multi-dendrites growth of Ni-Cu alloys in a forced flow. The morphologies of den-drites and distribution of temperature and concentration is studied. The result shows that fluid flow alters the local heat and concentration transfer at the solidification front, and effects the growth of the dentrite. Because of the undercooled melt flushing, the temperature and concentration of the upstream dendrite are low, making the tip of dendrite to grow faster; the temperature and the concentration of the downstream dendrite are high, making the tip of dendrite to grow slow. Due to the flow and multi-dendrites affect each other the crystal grows into asymmetrical dentrite morphologies. In addition, the fluid flow changed the preferred growth direction of dendrite which is not parallel to flow, making it tilts towards the upstream direction.%采用耦合溶质场、温度场和流场的相场模型,对Ni-Cu合金凝固过程中多枝晶生长进行模拟,研究了多枝晶生长形貌及温度场和溶质场分布.结果表明:熔体流动显著改变凝固前沿的传热和传质,从而影响枝晶生长.受过冷熔体冲刷,枝晶逆流侧前沿溶质浓度和温度低,枝晶臂尖端生长迅速；枝晶顺流侧前沿溶质浓度和温度高,枝晶臂尖端生长缓慢.在熔体流动和多枝晶之间相互影响下,枝晶呈现非对称生长.此外,熔体流动改变非流动方向枝晶臂的优先生长方向,使其向逆流方向倾斜.
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